Can I add tap water to starter once i pitched yeast?

Hi everybody! I know this is a noob mistake/question but after I boiled my DME into two cups of water to make a yeast starter, I cooled the wort down and pitched the yeast. I did not take into account water loss from the boil and was short by 1/2 cup of water. Without thinking, I added another 1/2 of tap water to bring the "wort" to 2 cups. I guess my question is, is it ok to add cool tap water to a yeast starter after the yeast was pitched. I added the tap water about 15 minutes after I pitched the yeast. Please let me know if I ruined/contaminated the starter.

I never factor it in when I'm making my starters. I would just leave it as is.

Its tough to say did you contaminated your starter or not.
Adding more water you decreased gravity but I"m sure its not big deal since volume is small, and all OG"s between 1.030 and 1.040 are acceptable.

I would do the three step check, crash cool, decant spent wort saving it in another container. Then smell it taste it and take a SG reading. Anything odd like it tasting really bad rotten etc. It should taste oxidized but not funky, oldy sweet and dry but not overly acidic. I've been tasting my starters since I started making them so I know what they are meant to taste like anything different I don't pitch the yeast (only once has it happened). Check gravity 1.001 or less then I would be concerned, wild yeast and bacteria can be veracous in their appietite

In the end chances are you will be fine. Yeast make the wort even more acidic than when they found it and this makes it impossible for bacteria to survive, no known pathogens can survive in beer. Hence why it has been the drink of choice for over 6000 years Wild yeast and other fungi are your concern but as it is a small amount of water and you pitched such a large amount of yeast your should be fine.

Do the checks if they are OK cross your fingers, wave garilic about like mad man and you will be fine.

It goes without saying next time let it ride.


Clem

Thanks Clem! Really helpful response.